Extended Iterative Scheme for QCD: the Four-Gluon Vertex

We study the self-consistency problem of the generalized Feynman rule (nonperturbatively modified vertex of zeroth perturbative order) for the 4-gluon vertex function in the framework of an extended perturbation scheme accounting for non-analytic coupling dependence through the Lambda scale. Tensorial structure is restricted to a minimal dynamically closed basis set. The self-consistency conditions are obtained at one loop, in Landau gauge, and at the lowest approximation level (r=1) of interest for QCD. At this level, they are found to be linear in the nonperturbative 4-gluon coefficients, but strongly overdetermined due to the lack of manifest Bose symmetry in the relevant Dyson-Schwinger equation. The observed near decoupling from the 2-and-3-point conditions permits least-squares quasisolutions for given 2-and-3-point input within an effective one-parameter freedom. We present such solutions for N_F=2 massless quarks and for the pure gluon theory, adapted to the 2-and-3-point coefficients determined previously.Comment: 46 pages, 11 figure

Extended Iterative Scheme for QCD: Three-point Vertices

In the framework of a generalized iterative scheme introduced previously to account for the non-analytic coupling dependence associated with the renormalization-group invariant mass scale Lambda, we establish the self-consistency equations of the extended Feynman rules (Lambda-modified vertices of zeroth perturbative order) for the three-gluon vertex, the two ghost vertices, and the two vertices of massless quarks. Calculations are performed to one-loop-order, in Landau gauge, and at the lowest approximation level (r=1) of interest for QCD. We discuss the phenomenon of compensating poles inherent in these equations, by which the formalism automatically cancels unphysical poles on internal lines, and the role of composite-operator information in the form of equation-of-motion condensate conditions. The observed near decoupling of the four-gluon conditions permits a solution to the 2-and-3-point conditions within an effective one-parameter freedom. There exists a parameter range in which one solution has all vertex coefficients real, as required for a physical solution, and a narrower range in which the transverse-gluon and massless-quark propagators both exhibit complex-conjugate pole pairs.Comment: 28 pages, 7 figure

The Higgs - photon - Z boson coupling revisited

We analyze the coupling of CP-even and CP-odd Higgs bosons to a photon and a Z boson in extensions of the Standard Model. In particular, we study in detail the effect of charged Higgs bosons in two-Higgs doublet models, and the contribution of SUSY particle loops in the minimal supersymmetric extension of the Standard Model. The Higgs-$\gamma Z$ coupling can be measured in the decay $Z \to \gamma$+Higgs at $e^+e^-$ colliders running on the Z resonance, or in the reverse process Higgs $\to Z \gamma$ with the Higgs boson produced at LHC. We show that a measurement of this coupling with a precision at the percent level, which could be the case at future $e^+e^-$ colliders, would allow to distinguish between the lightest SUSY and standard Higgs bosons in large areas of the parameter space.Comment: 18 pages LaTex + 7 figures (ps). Typo corrected in eq.(5

Analytic properties of the Landau gauge gluon and quark propagators

We explore the analytic structure of the gluon and quark propagators of Landau gauge QCD from numerical solutions of the coupled system of renormalized Dyson--Schwinger equations and from fits to lattice data. We find sizable negative norm contributions in the transverse gluon propagator indicating the absence of the transverse gluon from the physical spectrum. A simple analytic structure for the gluon propagator is proposed. For the quark propagator we find evidence for a mass-like singularity on the real timelike momentum axis, with a mass of 350 to 500 MeV. Within the employed Green's functions approach we identify a crucial term in the quark-gluon vertex that leads to a positive definite Schwinger function for the quark propagator.Comment: 42 pages, 16 figures, revtex; version to be published in Phys Rev

Probing scalar-pseudoscalar mixing in the CP violating MSSM at high-energy e+e−e^+e^- colliders

We study the production processes $e^+e^-\to H^0_iZ$, $H^0_iH^0_j$ and $H^0_i\nu_e\overline \nu_e$ in the context of the CP violating MSSM. In a given channel we show that the cross-section for all i (=1,2,3) can be above 0.1 fb provided M_{H_{2,3}}\la 300 GeV. This should be detectable at a Next Linear Collider and would provide evidence for scalar-pseudoscalar mixing.Comment: 17 pages, RevTex, 4 ps figures, figure 4 changed, minor modifications to text, version to appear in PR

Resumming the color-octet contribution to e+ e- -> J/psi + X

Recent observations of the spectrum of J/psi produced in e+ e- collisions at the Upsilon(4S) resonance are in conflict with fixed-order calculations using the Non-Relativistic QCD (NRQCD) effective field theory. One problem is that leading order color-octet mechanisms predict an enhancement of the cross section for J/psi with maximal energy that is not observed in the data. However, in this region of phase space large perturbative corrections (Sudakov logarithms) as well as enhanced nonperturbative effects are important. In this paper we use the newly developed Soft-Collinear Effective Theory (SCET) to systematically include these effects. We find that these corrections significantly broaden the color-octet contribution to the J/psi spectrum. Our calculation employs a one-stage renormalization group evolution rather than the two-stage evolution used in previous SCET calculations. We give a simple argument for why the two methods yield identical results to lowest order in the SCET power counting.Comment: 27 pages, 7 figure

Subanesthetic ketamine treatment promotes abnormal interactions between neural subsystems and alters the properties of functional brain networks

Acute treatment with subanesthetic ketamine, a non-competitive N-methyl-D-aspartic acid (NMDA) receptor antagonist, is widely utilized as a translational model for schizophrenia. However, how acute NMDA receptor blockade impacts on brain functioning at a systems level, to elicit translationally relevant symptomatology and behavioral deficits, has not yet been determined. Here, for the first time, we apply established and recently validated topological measures from network science to brain imaging data gained from ketamine-treated mice to elucidate how acute NMDA receptor blockade impacts on the properties of functional brain networks. We show that the effects of acute ketamine treatment on the global properties of these networks are divergent from those widely reported in schizophrenia. Where acute NMDA receptor blockade promotes hyperconnectivity in functional brain networks, pronounced dysconnectivity is found in schizophrenia. We also show that acute ketamine treatment increases the connectivity and importance of prefrontal and thalamic brain regions in brain networks, a finding also divergent to alterations seen in schizophrenia. In addition, we characterize how ketamine impacts on bipartite functional interactions between neural subsystems. A key feature includes the enhancement of prefrontal cortex (PFC)-neuromodulatory subsystem connectivity in ketamine-treated animals, a finding consistent with the known effects of ketamine on PFC neurotransmitter levels. Overall, our data suggest that, at a systems level, acute ketamine-induced alterations in brain network connectivity do not parallel those seen in chronic schizophrenia. Hence, the mechanisms through which acute ketamine treatment induces translationally relevant symptomatology may differ from those in chronic schizophrenia. Future effort should therefore be dedicated to resolve the conflicting observations between this putative translational model and schizophrenia

Corporeality, equality and education. A biopedagogical perspective

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The Clean Power Plan: Issues to Watch

Although the Clean Air Act is an imperfect tool for addressing the nation’s greenhouse gas emissions, it is the only available federal mechanism for directly addressing power plant carbon emissions. The Obama Administration’s Clean Power Plan, published in final form in August 2015, tackles the challenge. This paper from the Center for Progressive Reform (CPR) compiles 13 separately authored essays from 11 CPR Member Scholars, each addressing a different topic related to the Clean Power Plan, and each representing the expertise and views of its individual author(s). Published in July 2015, just before the release of the final rule, the essays tee up key questions about the rule’s legality, implications for the energy sector, and a series of discrete implementation questions, including the role of cap-and-trade (and offsets), the nature and distribution of state targets, and implications for environmental justice

The Clean Power Plan: Issues to Watch

Although the Clean Air Act is an imperfect tool for addressing the nation’s greenhouse gas emissions, it is the only available federal mechanism for directly addressing power plant carbon emissions. The Obama Administration’s Clean Power Plan, published in final form in August 2015, tackles the challenge. This paper from the Center for Progressive Reform (CPR) compiles 13 separately authored essays from 11 CPR Member Scholars, each addressing a different topic related to the Clean Power Plan, and each representing the expertise and views of its individual author(s). Published in July 2015, just before the release of the final rule, the essays tee up key questions about the rule’s legality, implications for the energy sector, and a series of discrete implementation questions, including the role of cap-and-trade (and offsets), the nature and distribution of state targets, and implications for environmental justice